Clinical Question

Is there a survival benefit to targeted temperature management at 33°C or 36°C in out-of-hospital cardiac arrest patients who remain unconscious after return of spontaneous circulation?

Conclusion

In unconscious survivors of out-of-hospital cardiac arrest of presumed cardiac cause, hypothermia at a targeted temperature of 33°C did not confer a benefit compared with a targeted temperature of 36°C.

Marjor Points

Therapeutic Hypothermia, define as deliberate cooling of a patient to 32-33.9°C (90-93F) who has no return of spontaneous neurologic activity after cardiac arrest. The goal is to reduce the repercussion injury to the brain which may be related to free radical formation, micro and macro circulation disruption and protease activation. At therapeutic temperatures the disruption of inflammatory and damaging cascades within the brain are thought to be decreased. [1] In patients who have been successfully resuscitated after cardiac arrest due to ventricular fibrillation, therapeutic mild hypothermia increased the rate of a favorable neurologic outcome and reduced mortality.[2]

The HACA Trial (Hypothermia after Cardiac Arrest) randomized patients after witness Ventricular Fibrillation (VF) and pulseless Ventricular Tachycardia (VT) to 32-34°C Hypothermia. There was a significant patient centered outcome and 6 month mortality decrease in the hypothermia group. A later trial by Bernard et. al. demonstrated similar benefit as did the Cochrane review. The TTM Trial (33°C vs 36°C) found similar mortality and morbidity benefits however 33°C may not confer benefit over 36°C.[1][3][4]

Standard care established by the ACCF/AHA 2013 guidelines, recommend therapeutic hypothermia for any comatose patient with a STEMI and out of hospital cardiac arrest from VF or puleless VT[5]

Although use of prehospital cooling reduced core temperature by hospital arrival and reduced the time to reach a temperature of 34°C, it did not improve survival or neurological status among patients resuscitated from prehospital VF or those without VF.[6]

In comatose children who survived out-of-hospital cardiac arrest, therapeutic hypothermia, as compared with therapeutic normothermia, did not confer a significant benefit in survival with a good functional outcome at 1 year. [7]

Baseline Characteristics

Average Age: 81

Sex: 83% Male

Cardiac Arrest Location: 53% at Home, 41% Public location

Bystander Witness: 89.5%

Shockable Rhythm: 80%

Asystole: 56%

Time from Cardiac Arrest: 1 min

Interventions

Patients were randomized to either 33°C or 36°C
The core body temperature was set as quickly as possible at the predefined target temperature, according to intervention allocation, with 4°C intravenous solutions, 43 ice – packs 8, 44 and commercially available cooling devices 45 at the discretion of the treating physician . The target core temperature was then maintained for 24 h. After the maintenance period core temperature was gradually raised to normothermia of 37°C during 8 hours with a rewarming rate of 0.5°C/hour in both groups.

Body temperature was then maintained at normothermia 37 ±0.5°C until 72 hours from sustained ROSC in both treatment groups, as long as the patient was in the ICU, using pharmacological treatment and temperature management systems when applicable